G-protein coupled receptors (GCRs) mediate fundamental processes in neurons including the regulation of excitability, neurotransmitter release, and gene expression. Recent studies suggest that GCRs are localized discretely both at the neuroanatomical and subcellular levels. The proposal presents evidence for the existence of a subcellular compartment in neurons enriched with a particular GCR, the A subtype of the alpha2-adrenergic receptor. The studies outlined herein will test the hypothesis that this compartment is specialized for the subcellular transport and processing of GCRs. The relevance of these studies lies in the possibility that the localization of GCRs to particular neuronal domains may be mediated by such subcellular compartments. Electron and light level immunocytochemistry, immunoisolation procedures, and cell biological techniques will be used to characterize the morphology, protein composition, and trafficking of this intracellular compartment. A neuronal cell line, GT1, will be used as a model system because the intracellular GCR-enriched compartments have been observed in these cells. The neuronal phenotype of GT1 cells permits the study of subcellular transport processes unique to neuronal systems.